Tribesmen hold pieces of a missile at the site of a drone attack in Mir Ali, Pakistan, on Jan. 24, 2009 -- just days after President Barack Obama's inauguration.

By Chris Woods, The Bureau of Investigative Journalism

Updated at 10:05 a.m. ET: LONDON -- Two U.S. reports published Tuesday provide significant insights into President Obama’s personal and controversial role in the escalating covert U.S. drone war in Pakistan, Yemen and Somalia.

In a major extract from Daniel Klaidman’s forthcoming book Kill Or Capture, the author reveals extensive details of how secret U.S. drone strikes have evolved under Obama – and how the president knew of civilian casualties from his earliest days in office.

The Times' report also reveals that President Obama "embraced" a broadening of the term "civilian", helping to limit any public controversy over "non-combatant" deaths.

As the Bureau's own data on Pakistan makes clear, the very first covert drone strikes of the Obama presidency, just three days after he took office, resulted in civilian deaths in Pakistan. As many as 19 civilians – including four children – died in two error-filled attacks.

Until now it had been thought that Obama was initially unaware of the civilian deaths. Bob Woodward has reported that the president was only told by CIA chief Michael Hayden that the strikes had missed their High Value Target but had killed "five al Qaeda militants."

Now Newsweek correspondent Daniel Klaidman reveals that Obama knew about the civilian deaths within hours. He reports an anonymous participant at a subsequent meeting with the president: "You could tell from his body language that he was not a happy man." Obama is described aggressively questioning the tactics used.

Yet despite the errors, the president ultimately chose to keep in place the CIA’s controversial policy of using "signature strikes" against unknown militants. That tactic has just been extended to Yemen.

On another notorious occasion, the article reveals that U.S. officials were aware at the earliest stage that civilians – including "dozens of women and children" – had died in Obama’s first ordered strike in Yemen in December 2009. The Bureau recently named all 44 civilians killed in that attack by cruise missiles.

'I'd have to go to confession'No U.S. officials have ever spoken publicly about the strike, although secret diplomatic cables released by Wikileaks proved that the U.S. was responsible. Now Klaidman reveals that Jeh Johnson, one of the State Department’s senior lawyers, watched the strike take place with others on a video screen:

"Johnson returned to his Georgetown home around midnight that evening, drained and exhausted. Later there were reports from human-rights groups that dozens of women and children had been killed in the attacks, reports that a military source involved in the operation termed “persuasive.” Johnson would confide to others, “If I were Catholic, I’d have to go to confession.”

Klaidman describes a world in which the CIA and Pentagon constantly push for significant attacks on the U.S.’s enemies. In March 2009, for example, then Chairman of the Joint Chiefs of Staff Mike Mullen reportedly called for the bombing of an entire training camp in southern Somalia in order to kill one militant leader.

One dissenter at the meeting is said to have described the tactic as "carpet-bombing a country." The attack did not go ahead.

Obama is generally described as attempting to rein back both the CIA and the Pentagon. But in the case of Anwar al-Awlaki – "Obama’s Threat Number One" – different rules applied.

An American-born cleric killed in Yemen played a "significant operational role" in plotting and inspiring attacks on the United States, U.S. officials said Friday. Anwar al-Awlaki was implicated in a botched attempt to bomb a Detroit-bound plane in 2009. NBC's Jim Miklaszewski reports.

According to Klaidman, Obama let it be known that he would consider allowing civilian deaths if it meant killing the U.S.-Yemeni cleric. "Bring it to me and let me decide in the reality of the moment rather than in the abstract," an aide recalls him saying. No civilians died that day, as it turned out.

In its own major investigation, the New York Times examines the secret US 'Kill List' – the names of those chosen for death at the hands of US drones. The report is based on interviews with more than 36 key individuals with knowledge of the scheme.

"[Obama's] first term has seen private warnings from top officials about a 'Whac-A-Mole' approach to counterterrorism; the invention of a new category of aerial attack following complaints of careless targeting; and presidential acquiescence in a formula for counting civilian deaths that some officials think is skewed to produce low numbers."

It is often been reported that President Obama has urged officials to avoid wherever possible the deaths of civilians in covert U.S. actions in Pakistan and elsewhere. But reporters Jo Becker and Scott Shane reveal that Obama "embraced" a formula understood to have been devised by the Bush administration:

"Mr. Obama embraced a disputed method for counting civilian casualties that did little to box him in. It in effect counts all military-age males in a strike zone as combatants, according to several administration officials, unless there is explicit intelligence posthumously proving them innocent."

So concerned have some officials been by this "false accounting" that they have taken their concerns direct to the White House, according to the New York Times.

The revelation helps explain the wide variation between credible reports of civilian deaths in Pakistan by the Bureau and others, and the CIA’s claims that it had killed no "non-combatants" between May 2010 and September 2011 – and possibly later.

Msnbc terrorism analyst Evan Kohlmann discusses why the death of Anwar al-AwlakiÂ is a big blow to future al-Qaida operations in America.

The investigation also reveals that more than 100 U.S. officials take part in a weekly "death list" video conference run by the Pentagon, at which it is decided who will be added to the U.S. military’s kill/ capture lists. "A parallel, more cloistered selection process at the CIA focuses largely on Pakistan, where that agency conducts strikes," the paper reports.

But according to at least one former senior administration official, Obama’s obsession with targeted killings is "dangerously seductive." Retired admiral Dennis Blair, the former US Director of National Intelligence, told the paper that the campaign was:

"The politically advantageous thing to do — low cost, no US casualties, gives the appearance of toughness. It plays well domestically, and it is unpopular only in other countries. Any damage it does to the national interest only shows up over the long term."

Clarification: An earlier version of this story said that President Obama "personally authorized the broadening of the term 'civilian'" and attributed the redefining of "civilian" to his administration. However, The Bureau of Investigative Journalism now understands that the Obama administration instead embraced a pre-existing policy introduced under President George W. Bush. The Bureau apologizes for this error.